Light-emitting diode (LED) devices have many diverse applications. For example, they are used as light sources for scanners, projectors, liquid crystal displays, fascias, traffic lights, etc. Compared with conventional light sources, such as incandescent lights, LED devices have numerous advantages, including compact size, long lifespan, low driving voltage/current, high structural strength, no mercury content (so less pollution when disposed of), high luminous efficiency for energy savings, etc.
LED devices typically include at least one surface-mount type LED package with an LED chip therein. LED packages including a pre-molded lead frame to carry the LED chip, instead of a conventional ceramic substrate, have been proposed. A pre-molded lead frame includes an insulating molding material encapsulating a lead frame having positive and negative electrical contacts exposed from the molding material.
Unfortunately, the bond between the lead frame and the molding material tends to be relatively weak, and the difference between the coefficients of thermal expansion (CTE) the lead frame and the molding material is very large. Because of the CTE mismatch, stresses are induced at the interface between the lead frame and the molding material as the conventional package experiences temperature cycling. The stresses, in turn, result in the delamination between the lead frame and the molding material when, for example, the LED package is surface-mounted to a printed wiring board during A solder reflow process. The LED package may subsequently be damaged by exposure to air or moisture through the delamination site.